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Research Interests

Regulation of ciliary dynein activity and assembly, and the role of the central pair complex in ciliary motility regulation.

Publications

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Research Abstract

Dynein and kinesin ATPases are molecular motors for many types of microtubule-based cell motility, including mitosis, directed transport of vesicles, maintenance of the endoplasmic reticulum and Golgi apparatus, and motility of (eukaryotic) cilia and flagella. We study the role of dyneins in microtubule sliding and eukaryotic flagellar bend formation, and in the regulation of flagellar waveform and beat frequency, through a combination of genetic, biochemical, and molecular approaches. While the role of dyneins as microtubule-associated motors for both ciliary and cytoplasmic motility is well recognized, little is known about their regulation or their mode of attachment to the loads they carry (vesicles or chromosomes in the cytoplasm, doublet microtubules in cilia and flagella). Our experimental system is the flagellated unicellular alga Chlamydomonas reinhardtii, since dynein subunits in Chlamydomonas flagella are homologous to subunits in mammalian dyneins but are more easily approached through genetic and molecular analyses. Human conditions that inhibit motility of these organelles (Kartagener''s syndrome, Primary Ciliary Diskinesia) are known to cause upper respiratory illnesses and male infertility. We are using in vitro mutagenesis and transformation of cloned genes to test specific hypotheses regarding the function of selected dynein subunits, and to understand mechanisms that regulate dynein assembly and activity. We are also using in vivo mutagenesis and selecting mutations that alter normal dynein function, characterizing these mutations at the molecular level, and correlating specific motility defects (analyzed by light microscopy) with defects in subunit structure and assembly. These studies provide the framework for determining general mechanisms of dynein assembly and function in all types of cell motility. The recent identification of kinesins associated with flagellar microtubules suggests that these motor proteins also play an important role in flagellar motility, and we are seeking to understand this role.

Little is known of dynein regulation in any cellular motility system, but the limited information suggests that kinase-phosphatase cascades are involved. In the flagellum, regulation is used to turn flagellar beating on and off, change beat frequency or waveform, and activate of dyneins in the precise patterns needed to propagate bends. In Chlamydomonas, flagellar motility is regulated in part by changes in intracellular calcium concentrations and some aspects of waveform regulation are known to involve protein kinase A-like and protein phosphatase I-like activities, but the mechanisms that link these changes to regulation of dynein ATPase activity are not known. We are selecting mutations that alter dynein regulation, as manifested by changes in flagellar beat parameters, and testing each mutation to see which signal transduction cascade has been altered and which flagellar structures are involved. Mutations that prevent dynein assembly into flagella are also analyzed to characterize genes that are important for cytoplasmic assembly of dynein subunits, targeting to the flagellar compartment, and attachment of dynein motors to doublet microtubules. These studies will provide key information about mechanisms that regulate the intracellular distribution and activity of dyneins.